[Nickle] substr("",0,0) ?

[Bart Massey]

Ok, you've just invoked
  substr("", 0, 0)
or in general
  substr(s, length(s), 0)
Nickle raises an illegal_argument exception because the
index is off the end.

Should it?  I contend no, because it makes writing string
algorithms without special cases harder.  But I can see the
argument.  Should it matter if the index is "just" off the
end, or should you be able to extract 0 characters from
anyplace?  I claim only just off the end, because that's the
only thing that makes any sense.

I guess my general intuition is that substring(s,m,n) should
be equivalent to
  chars->string(head(tail(string->chars(s), length(s) - m), n))
If that is the case, then the natural meaning of the
functions suggests that I am right above.

Discussion?  Or shall I call it a bug and fix it?

	Bart